1. Field of the Invention
The present invention relates to the field of detection apparatus used to screen individuals for the presence of explosives and other chemical entities.
2. Background Information
Security threats to the public dictate development of new technologies capable of rapidly detecting the presence of illicit and hazardous materials. Lead organizations such as the Department of Homeland Security (DHS) and the Transportation Security Agency (TSA) are responsible for ensuring safety of air travel and have invested significantly in developing technologies to combat the potential for attacks by explosive devices. Other venues that require screening include customs and port security. There is also a desire to screen other illicit materials such as drugs.
There are primarily two types of detectors used for screening baggage and people, explosive detection systems (EDSs) and explosives trace detectors (ETDs). Explosive detection systems (EDSs) detect bulk explosives hidden in checked baggage and frequently operate using dual x-ray tomography. Explosives trace detectors (ETDs) detect vapor or particles of explosives that are contaminated on people and the surface of baggage. ETDs are also used to resolve alarms from EDSs. Currently ETDs are used on a selective basis to screen for personal items and carry-on bags, but not for directly screening individuals. The lack of a capability to screen for explosives hidden on an individual is arguably the greatest vulnerability in aviation and homeland security. Though most of the attention for explosives threat detection is focused on aviation security, in fact security is an issue for many venues including other types of transportation, buildings, ports, stadiums, military bases and field operations, and in general any high traffic environment.
Personnel screening portals have been developed to screen individuals for concealed explosives and other materials. Several portal concepts using ETDs have been developed and tested and are referred to as explosives trace portals (ETPs). The most promising are based on non-intrusive (non-contact) removal of particles from clothing, followed by high-flow collection of the particles on the surface of a mesh or substrate; and then thermal desorption into an ETD. For example, U.S. Pat. No. 5,915,268 issued to Linker discloses a portal device that uses air jets to dislodge particles from a person and a downward flow of air to entrain and carry the particles to a concentrator device.
U.S. Pat. No. 6,073,499 issued to Settles discloses a passive method of particle collection that relies on the upward flow of air around people due to thermal conductivity in what is called a human thermal plume (HTP).
U.S. Pat. No. 6,708,572 issued to Jenkins discloses a similar method that uses air jets to assist the upward flow of the HTP. Each of these portal methods involve a flow of particle and vapor laden air and uses a concentration device that removes the target particles and vapor from the large volume of air by collecting them onto a mesh or substrate. The target particles and vapor are then thermally desorbed and mixed with a low volume flow of gas that leads to a chemical analyzer.
A two-stage concentrator for vapor/particle detection was disclosed by Linker and U.S. Pat. No. 6,345,545 issued to Brusseau. The two-stage concentrator enables concentrating particles in a high-volume gas flow to be efficiently coupled to a detector. The first stage of the concentrator contains a metal mesh for collecting particles and vapor that are entrained in the high-volume gas flow. The desorbed vapors from the first-stage concentrator are collected on the second-stage concentrator and provided to the detectors with a low-volume gas flow.
U.S. Pat. Appl. 2006/0196249 filed in the name of Syage and Hanold discloses a portal that screens multiple people with a single detector. In this configuration the process of collecting sample from people and transferring it to a concentrator are independent of the transfer of the sample from the concentrator to the detector. With this approach, sample can be effectively stored on a concentrator until the detector is ready to analyze it.
The chemical detectors used in all of the portals mentioned above use some form of ETDs including ion mobility spectrometry (IMS), mass spectrometry (MS), and gas chromatography/chemiluminescence (GC/CL) detectors. Other detectors may also be used.
An important characteristic of a personnel screening portal is fast operation to maximize the number of people screened by the portal. Current portals operate with a sampling interval of about 10-20 seconds from one person to another. This is much longer than the interval for standard metal detectors which range between 4-6 seconds. Methods to improve the sampling interval of a vapor/particle detecting portal are highly desirable.
It is also important that portals have reasonable upfront and recurring costs per unit. Given the large number of passenger lanes in U.S. and international airports (about 3000 each) and limited available budgets, inevitable compromises are made with regard to cost and the number of units that can be deployed. Furthermore current portals do not have the throughput capacity to handle other high flow transportation environments such as train and subways systems, and bus systems. Solutions that reduce the cost per passenger screened would allow greater distribution of deployed screening portals.